Various electromagnetic metering devices are known but none are completely satisfactory for handling granular materials. Devices opened and closed by a sliding action, such as a solenoid value, are often jammed by the granular material and are slow to open and close.
Co-pending U.S. patent application Ser. No. 07/779,075, now issued as U.S. Pat. No. 5,156,372 to one of the co-inventors herein, discloses electromagnetic metering devices which overcome these problems. The availability of reliable metering devices has led applicants to consider the solution of various dispensing problems using these electromagnetic metering devices.
Agricultural workers are frequently required to handle hazardous materials such as pesticides, herbicides, fungicides, fertilizers, and even treated seeds that present a hazard to the worker, co-workers, children, farm animals and the environment in general. Many hazardous materials are packaged in standard fifty-pound paper or plastic bags. Unused materials in unopened bags, opened bags, and in chemical hoppers increases the risk of accidental exposure at times when the unwary worker is not focused on the need to take precautions.
One setting where the worker is required to handle large quantities of hazardous materials is during the planting operation. In the planting operation, almost all soil insecticides are applied from a storage hopper carried on the subframe of a planting unit. Typically, an hour-glass type device is used to control the flow of insecticide from the storage hopper to the seed furrow. Rate selections are made by adjusting the diameter or flow area of the constriction zone. A meter wheel feeds the reservoir above the constriction zone in excess of flow needs and stops the flow when the planting unit is raised or the drive chain removed. Once the initial settings are made, flow rate from these devices is a function of time only. Therefore, the worker must determine the planting speed and stick to it to achieve planting rate accuracy. Further, there is great variation from one storage hopper to another and each row must be individually calibrated and rechecked periodically. Also, as the desired application rates are lowered, the accuracy of the hour-glass device becomes very erratic and eventually non-functional.
Those concerned with these and other problems recognize the need for an improved metering device for granular materials.